1. Field of the Invention
This invention relates to an efficient one-pot reaction process for the preparation of 2,3:4,5-bis-O-(1-methylethylidene)-β-D-fructopyranose sulfamate (topiramate) with the following chemical formula:

The invention also demonstrates a novel way for the purification of topiramate.
2. Description of the Related Art
Topiramate is a sulfamate substituted monosaccharide derivative which is useful in the treatment of epilepsy, obesity, bipolar disorder, neuropathic pain, migraine and smoking cessation. Topiramate acts as a carbonate dehydratase inhibitor, sodium channel blocker, AMPA antagonist, GABA agonist, and glutamate antagonist.
U.S. Pat. No. 4,513,006 discloses several processes for the preparation of topiramate. One of the described processes involves the reaction of protected fructopyranose with sulfuryl choride of the formula SO2Cl2 in the presence of a base in a dialkyl ether or methylene chloride solvent to produce the corresponding chlorosulfate:

The chlorosulfate may then be reacted with ammonia in a methylene chloride or acetonitrile solvent to produce topiramate. This process produces relatively low yields of the desired end product.
The European patent application EP 0 533 483 A2 describes a process according to the above described reaction sequence giving rise to improved yields of the desired product. According to EP 0 533 483 A2, the reason for the high yields is to particularly select reaction solvents from toluene, t-butyl methyl ether or tetrahydrofuran (THF) for the chlorosulfonation step, and from THF, t-butyl methyl ether, toluene and lower alkanol for the amination step as well.
PCT application WO 2004/041836 A1 discloses a continuous process for the preparation of topiramate using the above-mentioned chlorosulfonation step and amination step. This continuous process involves carrying out the chlorosulfonation step in a solvent selected from a cyclic ether, a straight or branched chain dialkyl ether, and an aromatic hydrocarbon, or a mixture thereof, particularly glyme. The amination step is carried out in a second organic solvent comprising at least the solvent used in the chlorosulfonation step, particularly in glyme.
However, the yields of topiramate obtained by the processes described before are still not satisfactory, particularly as far as bulk production is concerned.